Dynamoelectric machines, such as turbine/generators, typically have a rotor that is axially positioned within a stator core. The core comprises a plurality of axially thin annular laminations that are assembled together to form a cylindrical stator core. This core is supported within a stationary frame or housing, with the rotor disposed within the core. The rotor is formed as a cylindrical member having a central portion facing the stator core, and end shafts. An end face of the central portion is formed at the location of the shaft.
Field windings of the generator are mounted in slots machined in the body of the rotor, radially spaced from the shaft, the windings carrying DC (direct current) electricity. This current comes from a collector or exciter which is located at one end of the rotor and flows in axial leads that are positioned in a bore at the center of the generator shaft. The current is transmitted to the outer surface of the rotor shaft by a radial lead that is threaded into the axial lead. Attached to the top of the radial lead is a conductive member which transmits current from the radial lead to the field windings, which are held under retaining rings which support the windings on the rotor. One design of the conductive member is described in U.S. Pat. No. 4,870,308 issued on Sept. 26, 1989, which patent is assigned to the present assignee and is incorporated herein by reference.
Because the atmosphere surrounding the outer radial extremity of the radial lead conductor within the containment of the generator frame is a high pressure gas, typically hydrogen, used to cool the generator during its operation, it is necessary that a gas tight and leak resistant seal be provided. This is normally done where the radial lead conductor penetrates the rotor shaft to connect with the axial conductor. Also, because there is an electrical potential difference between the shaft and the field winding, this gas seal must also have certain minimum dielectric properties to minimize electrical leakage current flow from the field winding potential to the shaft ground potential.
A conventional method of insulating the radial lead conductor is performed by wrapping a glass cloth around the conductor until the required total electrical insulation thickness has been obtained. Typically, this glass cloth is impregnated with a "B" stage resin. Heat shrinkable material is then applied over the insulation to consolidate the insulation during the subsequent oven cure that chemically changes the B-stage resin and glass material into a consolidated structure around the radial lead conductor. An example of the use of a heat shrinkable insulation method can be found in application Pat. Ser. No. 147,703 filed on Jan. 25, 1988 and which is assigned to the present assignee. Such a typical insulation means for the radial lead conductor is shown in FIG. 1. The outside diameter of the consolidated insulation is then machined to required dimension and surface finish. As can be seen in FIG. 1, a void may occur with the insulation wrapping method due to the discontinuity formed at the area adjacent the beginning of the insulation wrap and the subsequent covering layers of insulation. Moreover, a required pre-tension of the wrap layers for the insulation is needed around the radial lead conductor to prevent hydrogen leakage. Furthermore, the outer surface of the insulation wrap may contain wrinkles after the oven cure due to the interaction of the heat shrinkable material wrapped over the insulation, causing a non-uniform inelastic compression across the thickness of the insulation wrap. Whereas such minor abnormalities may be acceptable in certain processes, the radial lead conductor insulation requires more exacting tolerances.